1. Field of the Invention
The present invention relates to a cushion unit arranged between a body and an axle of an automotive vehicle, and more specifically, to such a cushion unit that can control a height of the vehicle.
2. Description of the Background Art
Among the conventional cushion units provided between bodies and axles of the automotive vehicles, there have been available such cushion units that can adjust height of the vehicles. Japanese First (unexamined) Patent Publication No. 57-192643 discloses one of these, wherein a cylinder spring bracket is provided around an outer circumference of a cylinder of a hydraulic shock absorber, a rod spring bracket is provided around a piston rod via a spring bracket pressure chamber, and a suspension spring is interposed between those spring brackets. Further, a hydraulic oil is introduced into the spring bracket pressure chamber under pressure due to the extension/compression motion of the shock absorber to change a reactive force of the suspension spring so as to control the height of the vehicle.
In the foregoing conventional cushion unit, since the hydraulic fluid is not supplied to the spring bracket pressure chamber by a hydraulic pump or the like, but by using the extension/compression motion of the shock absorber, the cost of added apparatus is avoided.
However, in the foregoing conventional cushion unit, the hydraulic fluid in the cylinder is conducted to the spring bracket pressure chamber at every extension/on compression of the shock absorber so that the height control is executed even when such a height control is not necessary, leading to a possibility that the height control cannot be performed selectively only at the will of the driver.